Cathode ray tube manufacture

ABSTRACT

A SET OF SPACING FIXTURES ARE USED IN COMBINATION WITH THE SHADOWMASK AND THE SCREEN-CARRYING FACEPLATE OF A COLOR CATHODE RAY TUBE. THE FIXTURES ARE RELEASABLY SECURED TO THE SHADOWMASK FRAMING MEMBER DURING FORMATION OF THE MOSAIC SCREEN PATTERN, AND PROJECT OUTWARDLY BEYOND THE SHADOWMASK INTO CONTACT WITH THE EDGE OF THE GLASS PANEL OR FLANGE WHICH EXTENDS PERIPHERALLY AROUND AND FORMS PART OF THE FACEPLATE. THEY VIRTUALLY ELIMINATE THE POSSIBILITY OF THE SHADOWMASK MAKING CONTACT WITH THE FACEPLACE, THE THEREFORE PREVENT DAMAGE TO THE TUBE SCREEN.

NOV. 23, 1971 B, F PUNTEL l 3,621,545

CATHODE RAY TUBE MANUFACTURE Filed June 22, 1970 fm1/1, m

United States Patent lce Patented Nov. 23, 1971 U.S. Cl. 29-25.19 8 Claims ABSTRACT OIF 'THE DISCLOSURE A set of spacing fixtures are used in combination with the shadowmask and the screen-carrying faceplate of a color cathode ray tube. The fixtures are releasably secured to the shadowmask framing member during formation of the mosaic screen pattern, and project outwardly beyond the shadowmask into contact with the edge of the glass panel or flange which extends peripherally around and forms part of the faceplate. They virtually eliminate the possibility of the shadowmask making contact with the faceplate, and therefore prevent damage to the tube screen.

BACKGROUND OF THE INVENTION This invention relates to color cathode ray tubes and particularly to apparatus useful during manufacture of the patterned tube screens and assembly of the screencarrying faceplate with the tube shadowmask, a term used herein generically to denote mask structures having grids or apertures of any suitable type.

In the manufacture of color tubes the shadowmask and its associated mounting frame is mated with a particular faceplate assembly, which includes a screen panel and surrounding glass flange, and the mask is then used as the photographic aperture during photolithographic deposition of the three phosphors. During such use, as well as after completion of the patterned screen and final assembly of the tube parts, the mask is releasably secured Within the faceplate assembly, usually by means of leaf springs having one end connected to the mask frame and an apertured free end resiliently engaging a stud carried by the faceplate flange. By the use of three such spring and stud assemblies it is possible releasably to secure the mask with great accuracy within the faceplate assembly.

In accordance with a manufacturing sequence Well known in this art, a photosensitive phosphor slurry is applied to the faceplate panel, the mask is mounted in the manner mentioned above and a photoresist is exposed in a lighthouse The mask is then removed from the panel, the photoresist developed. This sequence of operations is followed at least once for each of the three phosphors which comprise the mosaic screen. In some operations a double application of each phosphor is employed to achieve the desired phosphor weight in the screen. This known type of manufacturing sequence requires that the mask be inserted into the faceplate assembly and removed therefrom at least three times, and possibly six times during the process of screen formation. Finally, after the phosphor deposition is completed and the faceplate aluminized, the shadowmask is inserted into the faceplate assembly where it remains in position for the life of the tube.

It is difficult to avoid mishandling the mask during assembly of the same with the faceplate, since the leaf springs are not then engaged with the studs carried by the faceplate. Damage resulting from contact of the mask with the faceplate has been a major problem in the industry. The phosphor screen is soft and fragile, and even the lightest contact between shadowmask and faceplate results in damage which requires that the entire faceplate panel be reclaimed and the photolithographic processes started anew. If the contact scratches the glass the panel is frequently damaged beyond repair. The shrinkage in tube yield which results from these difiiculties has proven to be a troublesome and expensive problem.

SUMMARY OF THE INVENTION My invention is based on recognition of the fact that during the manufacture of color cathode ray tubes they may readily be provided with exceedingly inexpensive means which virtually eliminates the problems. It is the general objective of the invention to prevent contact of the shadowmask and faceplate panel during assembly, and thereby substantially to eliminate the problem of damage to the phosphor screen. In accordance with this objective I provide a plurality of spacing fixtures each comprising a metallic strip one end of which is provided with means for releasably securing the strip to the mask framing member, and the opposite end of which extends laterally outwardly beyond the mask into contact With the tube faceplate assembly. It is preferable that all portions of the free edge of the glass flange surrounding the faceplate panel be coplanar, as well as the corner portions of the mask frame to which the fixtures are secured. Accordingly the fixtures hold all portions of the mask spaced from the faceplate and in proper position to accommodate securement of the leaf springs which mount the mask. In this way, the mask is prevented from contacting the faceplate during assembly and securement.

The invention, in one aspect, is featured by the simplicity with which the fixtures may be applied to and removed from the mask frame.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a plan View looking into a tube faceplateshadowmask assembly, the View showing the assembly as it appears during processing of the tube screen and before application of the tube bulb and neck;

FIG. 2 is a sectional View taken along the line 2-Z applied to FIG. l;

FIG. 3 is an enlarged sectional, perspective, illustration of a corner portion of the faceplate-shadowmask assembly; and illustrating in detail one of the fixtures of the invention and the manner in which it supports the assembly;

FIG. 4 is a side elevational view of a fixture in accordance with the invention; and,

FIG. 5 is an end elevational view of the fixture after adjustment to secure it to the shadowmask frame.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now making more detailed reference to drawing and initially to FIGS. l and 2 thereof, there is shown a typical color cathode ray tube faceplate-shadowmask assembly 10 which comprises a curved screen-carrying glass panel 11 having an upstanding glass flange 12 defining the periphery of the panel and terminating in free edge portions 13 which are preferably coplanar and are adapted for frit sealing to the bulb portion of the tube. The assembly is shown as it appears during processing of the tube screen, the usual mask-carried metal blades, or leaf springs 14 being resiliently engaged with studs 15 which project inwardly from glass fiange 12.

The shadowmask 16 comprises a thin sheet of metal, such as stainless steel, having a perforated center portion 17 curved and dimensioned to overlie the curved panel 11, and a peripheral frame 18 to which the leaf springs 14 are secured, as by welding. This frame lends rigidity to the mask. Preferably, and as shown, corner portions 19 of the frame 18 are coplanar and, when the mask is in position to be held by the leaf springs and studs, said corner portions reside at a level just below the level of the free edge 13 of glass flange 12.

In particular accordance with the invention, spaced portions of the shadowmask 16, desirably said corner portions 19, support spacing fixtures each of which has readily releasable means 21 (FIGS. 3 to 5) for securing the fixture to the corner portion 19 of the shadowmask. Said means 21 are described in detail below. Each fixture comprises an elongated metallic strip the inner end of which carries the securing means 21 and the outer end of which is adapted closely to overlie the free edge 13 of glass flange 12, during insertion of the shadowmask within the faceplate, and to support said mask just prior to snap-engagement of the leaf springs 14 with the studs 15. It is at this time, when the springs are not in contact with the studs and the mask is being inserted into or removed from the faceplate, that damage to the screen is most likely to occur.

In the broader aspect of the invention, any convenient type of securing means may be employed. However I prefer, and have illustrated, securing means 21 which takes the form of an expandable plastic fastener of the kind in which a cluster of resilient lingers 23 extend from a mounting ring 24 and are adapted to be spread by a rod 25 which can be forced through the fastener by pressure against finger piece 26, all as will be understood by comparison of FIGS. 4 and 5. As shown in those figures the fixture 20 is provided with an aperture of a size forceably to receive the resilient cluster of fingers 23, prior to expansion of the latter. The mounting ring 24 is too large to be forced through the aperture and overlies the upper side of the fixture. The mask frame is provided in each corner portion 19 thereof with an aperture, one of which is shown in FIG. 1 at 27. This aperture has a central, generally circular, portion through which the resilient cluster 23 may project, and a pair of opposed cutouts 27 to receive locating fingers 28 which depend from the fixture 20, as appears in FIGS. 4 and 5, and prevent swinging movement of the fixture with respect to the shadowmask frame.

As shown fragmentarily in FIG. l, and sectionally in FIGS. 2 and 3, the curved panel portion 11 of the faceplate assembly carries the patterned phosphor screen 22. As noted above, patterned screens of this type are prepared by photolithographic deposition techniques-there are several known methodsand it is at this point in the manufacturing sequence that the particular utility of the fixtures arises. In accordance with such techniques the inner surface of the panel 11, having thereon a coating of light-sensitive substance comprising a desired phosphor, is exposed in a so called lighthouse to a point source of light which is directed to pass through the openings in the adjacent shadowmask and impinge on the screen coating 22. Development of the screen area then produces a first screen pattern of spaced electron-responsive areas susceptible of predetermined color fiuorescence. As will be understood, this process is repeated a sufficient number of times to produce the triplets of tri-color phosphor dots characteristic of such a screen.

In accordance with this invention, and to prevent mishandling of the mask during assembly of the same with the faceplate and subsequent removal of the mask therefrom, a plurality, preferably four, of the fixtures 20 are associated with the mask and faceplate in the manner clearly appearing in FIG. 3. With the finger piece 26 in the withdrawn position (FIG. 4), the cluster of fingers 23 is inserted within the central circular portion of mask frame aperture 27, with the fixture-carried tabs 28 located within the aperture areas 27. The finger piece is then depressed to the position shown in FIG. 5, with the result that the resilient cluster is spread. The tolerance between the frame aperture 28 and the cluster 23 is such that spreading of the cluster secures the fixture to the shadowmask frame. With the fixtures thus secured in each corner of the mask frame, said frame can be introduced within the faceplate and moved downwardly into position in which it may be precisely located and supported by engagement of the resilient leaf springs 14 with the studs 15. As will be understood, after each light exposure step in the process the resilient fingers are decoupled from the studs 15 and the frame is lifted free of the faceplate. Insertion and removal of the shadowmask is carried out as many times as may be required to cornplete the phosphor screen 22. Throughout this entire procedure the fixtures 20 prevent contact between the shadowmask and the phosphor screen, since the outboard portions of such fixtures bear against the glass fiange of the faceplate. In this way screen damage is avoided.

When the screen has been fabricated, and it is desired to complete the tube by application of the bulb and neck portion, the finger piece 26 is drawn upwardly thereby reducing the spread of cluster 23 and the fixtures are removed frorn the mask and retained for reuse. At this stage of the process the shadowmask remains within the faceplate for the life of the tube, retained in place by the cooperating spring leaves and mounting studs.

I claim:

1. In combination with the shadowmask and the screencarrying glass faceplate of a color cathode ray tube; means for preventing the shadowmask from contacting the tube screen during manufacturing of the tube, with resultant damage to the screen, said means comprising: a plurality of members each of Which is removably secured to a corresponding portion of the shadowmask and projects from the shadowmask into contact with the free edge of a faceplate support flange which extends along the periphery of the screen, said members being so shaped, and disposed in contact with said support flange, as to prevent contact of the shadowmask with the faceplate screen while accommodating registration of the shadowmask with the faceplate area defined by the mentioned support ange.

2. A combination in accordance with claim 1, in which said faceplate support portion comprises a glass fiange extending peripherally around the faceplate and defining a recessed area carrying said screen, said members projecting outwardly beyond the shadowmask into contact with the edge of said flange.

3. A combination in accordance with claim 2, and further characterized in that each member is removably secured to a corresponding corner portion of the shadowmask.

4. A combination in accordance with claim 3, and further characterized in that each corner portion of the shadowmask is apertured, and each such member is provided With fastening means insertable within a corresponding aperture and expandable therein to maintain said members in assembled relation with the shadowmask.

5. In combination: a shadowmask having generally rectangular framing structure; and a plurality of spacing fixtures each having a first portion removably secured to a corresponding part of said framing structure, each said fixture further having a second portion projecting laterally outwardly beyond the shadowmask into position to overlie the free edge of the glass flange of a tube faceplate and thereby prevent contact of the shadowmask with such faceplate during assembly of the mask and plate.

6. A combination in accordance with claim 5, and further characterized in that each corner portion of said rectangular framing structure is provided with an aperture, and the said first portion of each fixture carries a fastening device projecting into a corresponding one of the mentioned apertures and expandable therein to maintain the fixture secured to said rectangular framing structure.

7. A fixture for use during photolithographic processing of the faceplates of color cathode ray tubes, said fixture being adapted for removable association with the framing member of a shadowmask and comprising: an elongated metallic strip one end of which is provided with means for releasably securing said one end in contact with such framing member; said fixture further having an opposite end portion adapted to extend outwardly beyond the shadowmask into contact with and to overlie the free edge of the flange of a tube faceplate, whereby to prevent contact of such shadowmask with such faceplate during assembly of the mask and plate.

8. A fixture in accordance with claim 7, and further characterized in that said means for releasably securing the xture takes the form of a resilient fastener insertable within an aperture formed in a shadowmask and expandable therein to maintain said xture in assembled relation with such shadowmask.

References Cited UNITED STATES PATENTS 2,883,677 4/1959 Geen 269--37 X 3,351,996 11/1967 Fiore 313-89 X 3,537,159 11/1970 Gartner et al. 29-25.19

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner 

